Japanese Patent Laid-Open No. 2007-164356, hereinafter JP 164356, discloses a position indicator in which a coil is provided at a position indicating part of the indicator to obtain a coordinate position by electromagnetic induction with a tablet. JP 164356 also discloses a position indicator in which an electrode (a conductor core) is provided at a position-indicating part to obtain an indicated position by capacitive coupling with a tablet.
In addition, JP 164356 discloses that a writing pressure detected inside a position indicator is converted to digital information, and a transmission signal is subjected to amplitude shift keying (ASK) modulation to transmit writing pressure information as the digital information. As a result, the position indicator can stably detect and transmit the writing pressure without suffering from external influences such as noise.
Moreover, JP 164356 discloses a position indicator that uses an electric double-layer capacitor as a power supply to extend the use of the position indicator with a single charge.
Furthermore, other position indicators using a capacitive system are disclosed in Japanese Patent Laid-Open No. Hei 07-295722 and Japanese Patent Laid-Open No. Hei 06-250772.
The above-described position indicators, which use a capacitive system, have a common characteristic that a tablet sensor is able to detect a position indicator (e.g., a stylus) and can be used also as a touch panel to detect an object (e.g., a finger).